16. Astronomers Find Huge Hole in Space

Astronomers have long known that at the largest scale, the universe looks like sea-foam: clusters of galaxies surrounding large, empty bubbles. Now researchers have found the biggest bubble of all—and at a mind-boggling 1 billion light-years across, it’s proving tough to fit into our understanding of how the universe evolved.

“There’s nothing special about this void, except nobody expected to find one this large,” says astronomer Lawrence Rudnick, who led the team that announced the void’s existence in March.

The puzzle first emerged when Rudnick, who had decided to study a large cold spot in the cosmic microwave background, found some strange data in a radio telescope survey of distant galaxies. A graduate student working with Rudnick made the connection between the survey and the microwave map: The cold spot corresponds to a region of the sky, 40 times the area of the full moon as seen from Earth, where relatively few galaxies have turned up. The microwave background marks the limit of the observable universe, nearly 14 billion light-years away, and Rudnick believes that the void, which is 6 billion to 10 billion light-years away, imprinted its form on the microwave background by the simple virtue of being empty: Under the influence of dark energy and gravity, space containing clusters of galaxies compresses microwaves to a shorter, warmer part of the spectrum, while space that is empty on this scale stretches and cools microwaves.

So far, this is the only supervoid to be detected (pdf), but if holes this large turn up more often, astrophysicists may have to reconsider theories of how large-scale structures in the universe formed.